all you'd establish is that people are biased toward the OT (which doesn't even preclude all people from speaking about it objectively).
it's a silly proposition to begin with. you're assuming two pairs of actors would deliver lines exactly the same way. not only that, but they have different voices... they're fundamentally different at that base level. what are you even doing? most people would prefer the OT cast anyway, even if you did somehow get these actors to perfectly imitate the other pair's delivery.
I am well aware of how the industry reacted to the movies. That was part of my point as to why Star wars is what it is today(I even acknowledge it in the post you quoted). It certainly isn't the dialogue and the acting.
In my opinion, if the Prequel trilogy releases first and we would be having this argument about 4, 5 and 6. But thats just me.
all you said was that it was a unique experience for the 70's. that's true, but that speaks more toward the audience's reaction in its phrasing. i'm talking about its effects on how films are bought, sold, and marketed and its effects on how people within the industry developed their projects.
star wars was designed to be a prototypical hero journey, so the prequels wouldn't have had the familiar archetypes and thematic resonance that made it such a universal hit. they'd be much darker and likely wouldn't have appealed to children on the same level as the OT. lucas has said the OT is about Vader, not Luke, which is somewhat true when you consider the prequels, but he painstakingly researched archetypal stories and recurring characters to tell a very specific story. i'm not sure if you were going to mention that quote of his, but i'm telling you just in case.
dialogue's not that bad. in some spots, sure, but on the whole it suits its purpose well. mostly pretty straightforward and simple. movie made for kids, etc., etc. one of the OT's greatest strengths is actually its characters. people have connected with the OT roster and that's primarily due to the actors' performances. according to you, it certainly isn't the witty dialogue. in order for those characters to achieve the immense cultural relevance they've acquired, they'd have to have done something right as far as their profession was concerned.